The invention relates to a leg prosthesis which is to be adapted to a thigh stump following amputation.
Basically, there is a distinction between passive and functional or active prostheses. Movements can be executed with the latter which imitate the natural sequence of motion of a healthy leg. The use of myoelectric controls would be theoretically conceivable for this. With these myoelectric controls myosignals are transcutaneously derived from innervated musculature, amplified and used for analog or digital control of electromotors, which can then execute appropriate prosthesis motions. Of course, the energy expenditure with a leg prosthesis is so high that the energy density of known accumulators would not suffice to be able to supply an electric drive motor for the knee joint with electric current for an acceptable period of time.
With so-called internal power prostheses, movements of distant body parts via bandage traction are used to carry out the prosthesis function. Thus, perhaps the forward movement of the shoulder on the non-amputated side can be used for opening the prosthetic hand. Nevertheless, up until now no attempts are known to design a leg prosthetic as an internal power prosthesis.
From U.S. Pat. No. 4,143,426 an implantable adapter is known, which has a porous surface, into which bone material is supposed to grow. This adapter is part of an internal power prosthesis, in which forces are transmitted to a joint via an artificial band. The forces generated originate from the remaining muscles of the carrier of the adapter itself.
From the publication H. H. Wetz et al., xe2x80x9cAmputation and Prosthetics,xe2x80x9d Orthopedics, 27:397-411 (1998), myokineplasty according to Sauerbruch is described, which is suitable for this. Shown therein is a connecting element in the form of a stirrup (FIGS. 18, 19 and 20a, b), which is supposed to transmit the forces generated by the muscle. However, in the publication this stirrup is tied to the pectoral muscle or the biceps muscle, thus in the shoulder or upper arm area.
Against this background, an object of the present invention is to develop a proposal for a leg prosthesis in the form of an internal power prosthesis. This object is accomplished in accordance with the invention by a leg exoprosthesis for adaptation to a thigh stump. Advantageous refinements and embodiments are described below and in the dependent claims.
Accordingly, the leg prosthesis comprises an adapter for a knee joint, the knee joint itself, and a lower leg prosthesis coupled to it, wherein the adapter with a proximal stem element, which is at least partially covered with an open-meshed, three-dimensional spatial network structure, is implantable into the tubular bone stump of the thigh stump and is provided on its distal end with a coupling device for the knee joint. A bridle with a connecting element attached on the thigh stump end in the form of a stirrup is coupled to the lower leg prosthesis for tying to the extensor musculature of the thigh, which transmits extensor forces for extending the knee joint.
The extensor forces are generated by the patient himself in the extensor musculature, for example in the quadriceps muscle. The tying of the force-transmitting element to the musculature on the amputation stump takes place according the so-called Sauerbruch myokineplasty.
For this purpose, a muscle channel is formed in the remaining musculature in the amputation stump. By turning a skin flap inwardly, a displaceable muscle channel is successfully laid out such that, for example, an ivory or a glass pin can be guided into it. The patient is in a position, owing to the innervation of the stump musculature, i.e., the quadriceps muscle, to apply appropriate forces and via the muscle canal and a corresponding connecting element to introduce them into the force-transmitting element, and thereby to extend the artificial knee joint appropriately. The connecting element installed on the thigh stump end in the form of a stirrup serves for this purpose.
The bridle mentioned as a force-transmitting element basically replaces the natural patellar ligament and the patellar attachment up to the tibial tuberosity in the healthy leg.
The adapter for the knee joint is installable with a proximal stem element into the tubular bone stump of the thigh stump, wherein the stem element is at least partially covered with an open-meshed, three-dimensional spatial network structure, and is provided on its distal end with a coupling device for the knee joint.
The open-meshed, three-dimensional spatial network structure, which is also characterized as interconnecting, makes it possible for natural bone material to grow into, through, behind and around it during the healing phase, so that the stem element is integrated into the tubular bone after a relatively short time, in any case with respect to the substrate flow, and an extremely stable secondary fixation is guaranteed.
By this construction a sufficiently firm seating of the adapter on or in the thigh stump is guaranteed, which can also withstand the high forces of up to 800 kp introduced into the force-transmitting element.
A previously unknown natural coordinated movement is possible with the leg prosthesis of the invention, owing to the tying of the remaining musculature in the thigh stump directly to the lower leg prosthesis coupled on the knee joint.
However, the knee joint is also constructed in a special way according to a preferred embodiment, and is adapted to the leg prosthesis of the invention. Thus, it is provided that the knee joint has an upper part, which is connectable with the adapter, and has a lower part which is flexibly connected with the upper part. The upper part is supported on the sliding surfaces of the lower part with skids, and the skids are held against the sliding surfaces by the action of a spring. The upper part is swivellable with the skids on the sliding surfaces around a pivot point until reaching an extended position, wherein the vertical main axis of the upper part is shifted forwardly (anteriorally) in relation to the vertical main axis of the lower part. In side view the skids basically have bearing surfaces which, when viewed from front to back (anterior to posterior), assume curvature radii which become ever smaller about the pivot point, and which lie on the sliding surfaces of the lower part, which are substantially flat in construction. The upper part is displaced to the rear (posteriorally) in relation to the lower part with increasing bending of the joint. Further details for this construction can be gathered from European patent EP 0 358 056 B1.
This knee joint is adapted, in an especially suitable manner, for use within the framework of the present invention. Thus, the special construction of the pole curve of the skids of the upper part with the curvature radii which, viewed from front to back, become continuously smaller, makes it possible to imitate the natural force conditions in the knee. Thus, the force transmitted by the force-transmitting element is greatest in the extended position of the knee and smallest in the flexed (bent) position. This corresponds to the natural conditions.
With a pole curve constructed other than as indicated, for example with a circular pole curve, the physiological course of movement of the knee would not be possible at all.
The knee joint known from the cited publication is adapted, in an especially advantageous manner, to use in the framework of the present invention, if the lower part of the knee joint has a frame which supports a carrier for the sliding surfaces, whose upper part is connected by axle journals with braces guided laterally on the frame. The braces are rigidly connected by an axle engaging through oblong holes, and the axle is biased in relation to the frame by a spring and via the braces holds the skids against the sliding surfaces of the lower part. The mentioned force-transmitting element is fastened on the frame of the lower part. The force generated by the quadriceps muscle is thus introduced directly from the thigh stump into the lower part of the knee joint under excess tension of the knee joint itself. This is an exact imitation of the introduction of force through the patellar ligament or patellar attachment in the healthy leg.